A disruption tolerant network is a wireless multi-hop network including a plurality of communication nodes. A disruption tolerant network can be called a delay tolerant network or a disconnect tolerant network. In the specification of the present application, disruption/delay/disconnect tolerant networks are collectively referred to as “DTNs”. In a DTN, a number of communication nodes (hereinafter referred to as “DTN nodes”) autonomously relay a message (data bundle or data packet), thereby achieving the delivery of the message from a source node to a destination node. One or both of the source node and the destination node may belong to the DTN (i.e., DTN node), or belong to an external network (e.g., the Internet, a public cellular network, or a wireless Local Area Network (LAN)). When one or both of the source node and the destination node belong to an external network, at least one of the DTN nodes serves as a router that relays messages between the DTN and the external network.
The DTN is based on the premise that temporary or intermittent loss of communications could occur due to movement of DTN nodes, blocking of radio signals caused by obstacles, or the like. In other words, the DTN is based on the premise that there is no stable communication path between the source node and the destination node at least at some point in time. To cope with temporary or intermittent loss of communications, each DTN node performs a store-and-forward operation. Accordingly, the DTN can also be called a store-and-forward type wireless multi-hop network. Some or all DTN nodes constituting a DTN may be mobile nodes having mobility. In this regard, the DTN can also be called a store-and-forward type wireless ad-hoc network. It has been assumed that DTNs may be used for emergency communications during a disaster, and for vehicle-to-vehicle communications and road-to-vehicle communications in Intelligent Transport Systems (ITS).
Patent Literature 1 discloses an improvement in message delivery between DTN nodes. Patent Literature 2 discloses an improvement in routing in a DTN.